The celestial “latitude”: an object’s angle north (+) or south (−) of the celestial equator, from +90° to −90°. Vega is at +38.8°, Sirius at −16.7°. From a given latitude, declination tells you whether an object is always up, never up, or rises and sets.
ToolsInteractive atlas, Celestial fix
Related terms
- Right ascension
The celestial “longitude”, counted eastwards along the celestial equator from the vernal equinox point, in hours from 0h to 24h (1h = 15°). With declination it fixes a star’s position on the celestial sphere. Abbreviated RA.
- Celestial equator
The projection of the Earth’s equator onto the sky, halfway between the two celestial poles; its declination is 0°. It rises due east and sets due west everywhere on Earth. Orion’s Belt lies very close to it.
- Circumpolar
Said of an object that never sets from a given place: it circles the pole without dipping below the horizon. That happens when its declination exceeds 90° minus your latitude, so +38.5° at 51.5° north. The Plough and Cassiopeia are circumpolar from the UK and France.
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